In general the present invention relates to the mounting of electrical and electronic equipment, and more particularly to a rack assembly for receiving plug-in modules, each module housing a portion of the electrical/electronic circuitry. Although the invention has utility in a wide variety of installations, in its preferred form it is particularly suited for mounting electrical and electronic circuits and components carried in an aircraft (such circuits and components being referred to herein as avionics equipment).
The mounting of electrical and electronic equipment many times requires ready accessibility of the circuit components and wiring, for testing and servicing. This is especially true for avionics equipment, where the proper operation of the equipment may be crucial to safe flight of the aircraft. It is therefore desirable to mount such equipment on supporting racks that are readily accessible to ground crews from the exterior of the aircraft when it is grounded and to the crew from the interior of the aircraft when in flight. Heretofore, the avionics equipment has not been easily accessible when airborne. And accessibility that has been provided, while airborne or grounded, has been restricted to the front of the equipment racks. In such installations, plug-in avionic units can be removed and reinserted from the fronts of the racks, but wiring at the rear of the racks is reachable only with difficulty by stretching an arm through from the front rack openings, thereby rendering certain repairs difficult, and others possible only after dismantling portions of the rack.
The construction of the racks and plug-in units is further complicated by the requirement that the electronic components in the units be cooled by circulating air through the units. Heretofore, the manner in which cooling air has been circulated, has not resulted in an efficient use of the available coolant. For example, there are: prior designs that force the air downwardly through the units against the natural convective flow of warm air; designs that circulate air past the components themselves thereby depositing particular contaminants carried by the air onto the electrical components, the build-up of contaminants impairing transfer of heat from the components to the coolant; and designs that unintentionally but inherently circulate the coolant proximate some components while by-passing others.
The avionics equipment is usually mounted in plug-in units, each removable for service, repair of replacement. In most prior art designs, considerable insertion and withdrawal forces have been required to overcome the friction forces that oppose the engagement and disengagement of the unit-mounted connector parts with the complemental rack-mounted connector parts. Mechanical lever devices carried on the front panel of the plug-in units and connectable to the fronts of racks have been provided to assist in achieving engagement and disengagement. However such mechanical assists have merely created new problems. For one, deformation of the housing of the plug-in unit (usually constructed of light-weight sheet metal) frequently results from loads placed thereon during operation of the mentioned levers. Such deformation can cause misalignment of pins on the connectors on the unit and the racks which in turn can cause damage to the pins and also increase the friction that must be overcome during insertion or withdrawal. To side-step this problem, the number of connector pins on each plug-in unit (and thus the number of electrical connections to and from the unit) has been limited.
An object of the present invention is to provide a plurality of equipment rack assemblies for avionics equipment, in which the racks are uniquely arranged within a lower lobe of an aircraft with ready access being provided both to the fronts of the racks where the modules can be removed and reinserted, and to the rears of the racks where the rack wiring is located.